The following research proposes to study the effect of a change in scientific knowledge on medical practice. Specifically, it will measure the consequences of the NHLBI Coronary Artery Surgical Study (CASS) results on subsequent utilization of cardiac surgery and related diagnostic procedures. In addition to examining trends in utilization data from the National Hospital Discharge Survey (NHDS), the utilization of Cardiovascular Nuclear Medicine Studies (CVNMS) by Bronx-based physicians will also be analyzed. CVNMS are non-invasive diagnostic procedures which are based for imaging of cardiac structure and function under controlled conditions. Patients with abnormal results may then be referred for cardiac catheterization, an invasive diagnostic procedure, which identifies patients who need and can undergo Coronary Artery Bypass Graft Surgery (CABGS). Since 1982, a standardized and detailed CVNMS request form has been in use by the hospitals of the Albert Einstein College of Medicine. The test request form asks the referring physician to select from three types of CVNMS, to indicate the reason for ordering the study, to indicate his present patient management plans, present course of medication, types of heart disease suspected, severity and types of symptoms, and to estimate what the study results are likely to show. These data will be compared for a one-year interval before and after the release of the CASS results. Opinions about patient management made by an expert panel of board certified cardiologists will also be analyzed. This research addresses the change in physician behavior following a change in a certain type of knowledge (i.e., the results of a major randomized clinical trial). In general terms, this study has implications for more general processes in medicine and science, related to dissemination of information, diffusion and adoption of innovations, technology assessment, peer review and reference groups.